There are several 漢字 in 漢文 that are common in modern Japanese, but can have incredibly different functions on a grammatical level. In particular, 所 and 者, which I will attempt to tackle in this post.
First of all, you should know that they do not really mean “place” and “person” respectively. They are used in this way, yes, but they are slightly (but very importantly) different. That is, 所 is often used to represent the one acted upon, and 者 is used to represent the actor.
Hard to understand, yes, so here’s an example.
Rulers are followed; they do not follow.
The juxtaposition is clear, if not a bit confusing at first.
君者： It seems entirely appropriate to translate this 者 as a person, but perhaps it would be better to think of it as a representation of the 本質 of 君. Similar to modern Japanese’s 君というのは.
所事也： Here 所 represents the destination of 事ふ, where the action of 事ふ is being channeled. See ex. below.
事人者： In contrast to the above, 者 comes last, not first, being modified by the 人に事ふ before it. It is the exact same as 君者 and means the exact same thing – that is, こと・の. Note, also, the contrast being made between 人 and 者. This is another clue that it does not exactly mean “person.”
You might be confused because it is not 事はる所なり, but 事ふ所なり. At first glance, the example seems to be saying “Rulers are followers; they are not followers.” But if you remember the distinct difference between 所 and 者, that is, the difference between the actee and the actor, it becomes clear. (It’s kind of understandable where the meanings of “place” and “person” came from, right?”
In addition, there are, in fact, 受身形 that explicitly use 所 to represent the object of the action. For example,
Before I give an admittedly awkward translation, I would like to explain the point of my giving this example. Namely, the bolded part is (just) one type of (many) 受身形. It is a set phrase, A、為B所C and is read A、BのCするところとなる (AはBにCされる). If we look at the example as a whole,
“There are three (systems) in a country. (Those) who control people, (Those) who are controlled by other people, and (Those) who neither control others nor are controlled by others.”
Well, that’s the gist of it. Note the parentheses. First of all, it’s clear that the 三制 is related to the other 制, but forced between an even more forced translation and just using another meaning of the character, I chose the easy way out. I’m not so sure it’s wrong, though (and part of the difficulty of 漢文 is figuring out just which meaning is being used). Also, I put “those” in parentheses, and I’ll give you a hundred points if you guess why.
If you said “because ‘those’ infers a human being and this 者 does not necessarily to the actual people performing the action, but the entirety of the situation” or something similar, Do pass Go, Do collect $200.
I’m satisfied with these two example sentences. I think they did very well in illustrating the difference between 所 and 者.
*Note: In regards to the example sentence above regarding 為A所B, there are times when 所 is abbreviated and it just appears as 為AB. Eg, 卒為天下笑 = 卒（つい）に天下の笑ひと為る. This is a form older than the one using 所 (maybe even the people of the time got fed up with how ambiguous this language was), and if we were to “fix” it, it would be 卒為天下所笑 = 卒に天下の笑ふ所と為る。 (An interesting way to think of this is that it is similar to the 連体形 in classical Japanese, in that a particle is often found directly after the verb because of the abbr. of a noun (like の). Eg, これやこの行くも帰るも別れては、知るも知らぬも逢坂の関 in which the 人 after each noun is abbreviated.